* I drop things. I don't mean to, but I do.
* I don't travel as much as I used to, but we've taken many road trips and airplane flights in the past and a case is so nice when you've got to put your Nook in one of those scanner trays at airport security, when you just need to toss it quickly in your carry on, etc.
* My wife and I both have the same make/model of e-readers so having different cases is really nice when you want to tell at a glance which one is on the coffee table and which one is the one you still can't find because maybe the cat knocked it off the table.
* I commute by bicycle, in all sorts of weather, and it's nice to know my e-reader (and phone) are covered in a case during uneven travel conditions.
* I've had my phone come out of my jersey pocket while riding down a hill and the phone bounced and skidded about a hundred feet before coming to a halt. Thanks to the case, it still worked, and though the case looked like it'd gone through the ringer, the phone was (and is) still fine.

Caveat: I like a case that my phone/ereader "wears" all the time, like a snap-on cover that you just flip back to use, I don't like a case where you have to extract the device to use it. For me, that just means I have two things to keep track of and/or lose, rather than just one.

Whether or not the reader is easier to hold with or without a case depends on the size/shape of the person's hands and the size/shape of the specific device.

True. I actually bought a few different cases for my Kindle Paperwhite. Even got one that had an elastic band on the inside cover where you can insert your hand. All of them added too much weight and thickness to my reader to be comfy. Honestly, I really like the feel of the PW3 sans case particularly with its "soft" matte back. Chassis may be plastic but it feels pretty solid/sturdy and it's actually withstood a several drops (granted all on carpet).

Mind, it's the opposite with my iPhones and iPads. Never been fond of the aluminum or glass back. Those just seem to slip easily from my fingers.

True. I actually bought a few different cases for my Kindle Paperwhite. Even got one that had an elastic band on the inside cover where you can insert your hand. All of them added too much weight and thickness to my reader to be comfy. Honestly, I really like the feel of the PW3 sans case particularly with its "soft" matte back. Chassis may be plastic but it feels pretty solid/sturdy and it's actually withstood a several drops (granted all on carpet).

Mind, it's the opposite with my iPhones and iPads. Never been fond of the aluminum or glass back. Those just seem to slip easily from my fingers.

Also, my ereader is a device used most often while sitting in my home where it's not in too much danger. My phone is carried out and about and has a much higher potential of being dropped on a hard surface, so I keep it in a sturdy case at all times.

* My wife and I both have the same make/model of e-readers so having different cases is really nice when you want to tell at a glance which one is on the coffee table and which one is the one you still can't find because maybe the cat knocked it off the table.

This made me smile, thanks It also reminded me of my browsing ebay for sleep covers for my new Clara HD. My Paperwhite (now my Dad's Paperwhite) is in the official Amazon sleep cover, and the extra weight and sturdiness is good for protection - first from my CP-induced clumsiness and now from his clumsiness, induced by 85 solar orbits. I do have the official Clara sleep stand cover, and like it a lot, but the Shenzhen clones offer some very interesting options visually that I think I might buy just to liven up the place from the sea of black/dark blue device covers everywhere

Always with a case.
I have a soft spot for turquoise, so a cover in such color adds to my Kobo's beauty

Borrowing a concept from IT, the question is not IF you will ever drop your eReader; the question is WHEN it will happen.
Hence my advice is "Always have a cover" (just like "Always have a backup of your data").

Have never used a case (unless you count Sony PRS-505 cover) for ten years now and daily carry my reader in a backpack. Have yet to break a device. My only damage comes from a small scratch on a Kindle PaperWhite2 when I brought it to the beach in Cuba and a grain of sand got between my finger and the screen when I swiped.

Edit: One more reason I don't like the typical cases is because of the magnets in the cover. When I have a few things in my bag, like tablet, reader and phone, the covers and devices use to take turns waking each other up with the @!#$%^&! magnets and drive me crazy.

I use a cheap case for my Kindle Oasis 2 and recommend using something to protect your device but be careful. Sometimes I worry that my case grips my device too strongly and may bend it to some degree, especially if you want to take it out semi-freqently etc. Carta e-ink screens are sensitive and after losing my DX to a cat napping on it I have been paranoid! Just to be safe I try to tuck mine under the pillow when I am sleeping and a case has been adequate to protect from falls for both my first and second generation Oasis e-readers. And as others have mentioned, if you go that far you might as well get something with a sleep cover or a sleeve. It all depends on your use.

I used to always keep my e-reader in a sleeve rather than a case, and I ring it everywhere with me.

I use a sleeve as well, I can tuck my glasses in the same sleeve as my Kindle. I also have skin on my Kindle Voyage. A case would just add to the weight while reading, and I would constantly lose my glasses

Looking at going to a larger Kobo, huge headache trying to find a larger sleeve made of neoprene without a zip. If anybody has seen one I would love a link.

I've always had cases on my ereaders. Currently waiting for a case to be delivered for my new KPW. I actually find it a bit hard using the device without a cover. Judging by the rather worn and battered look of the cover on my old KPW, i figure it extended the life of the device considerably. It also had a place to keep my pen and slots for notepaper, Sudoku etc.

When I get a new cell phone, I dont bother putting the SIM card in till I get a case. I order a case for a Kindle at the same time I order the Kindle. That's one of the reasons I returned my Oasis 2. When Kindle said their cases were intended to protect the device but rather to personalize them I decided the California Virus had infected them.